Method and apparatus for electronic device manufacture using shadow masks

ABSTRACT

Electronic devices are formed on a substrate that is advanced stepwise through a plurality of deposition vessels. Each deposition vessel includes a source of deposition material and has at least two shadow masks associated therewith. Each of the two masks is alternately positioned within the corresponding deposition vessel for patterning the deposition material onto the substrate through apertures in the mask positioned therein, and positioned in an adjacent cleaning vessel for mask cleaning. The patterning onto the substrate and the cleaning of at least one of the masks are performed concurrently.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and systems for fabricating electroniccircuits, and particularly to apparatus and methods incorporating shadowmasks and shadow mask cleaning in the manufacture of integratedcircuits.

2. Description of Related Art

Large area active electronic devices are widely used in flat paneldisplays and related technologies. For example, active matrix backplanesare used in flat panel displays for routing signals to pixels of thedisplay in order to produce viewable pictures. Active matrix backplanes,as well as other large area electronic circuits, are multilayer devicespresently manufactured using photolithography, a pattern definitiontechnique that uses electromagnetic radiation, such as ultravioletradiation, to expose a layer of a photoresist material deposited on thesurface of a substrate. Exemplary photolithographic processing steps toproduce a layer of a multilayer active matrix backplane on a substrateinclude: coat with photoresist, pre-bake, soak, bake, align, expose,develop, rinse, bake, deposit a layer, lift off the photoresist, scrub,rinse, and dry.

Photolithography-based manufacturing methods thus include a wide varietyof both additive (material deposition) steps and subtractive (materialremoval) steps, requiring large, complex and expensive fabricationfacilities that incorporate many disparate manufacturing technologies.Furthermore, many photolithographic manufacturing steps must be carriedout in clean room environments, further driving the manufacturingcomplexity and costs high.

Alternatively, a vapor deposition shadow mask process is well-known andhas been used for years in microelectronics manufacturing. The vapordeposition shadow mask process is a significantly less costly and lesscomplex manufacturing process, compared with photolithography-basedmanufacturing. The vapor deposition shadow mask process can be used toform one or more electronic devices on a substrate using additiveprocesses only. This is done by sequentially depositing patterns ofmaterials including conductors, semiconductors and insulators, throughcomplementary patterns of apertures in shadow masks positioned betweenone or more material deposition sources and the substrate.

One challenge in implementing all-additive process steps for the volumemanufacturing of electronic circuits is that as a shadow mask is usedrepetitively for patterning a material onto a substrate, the mask alsoaccumulates the material on its surface and in its pattern of apertures,changing the dimensions of the apertures and thereby degrading maskperformance for future depositions through that mask onto a substrate.Frequent replacement of a shadow mask, especially a large area mask,generally is neither practical nor cost-effective for a volumemanufacturing process. Some degraded shadow masks may be cleaned toremove deposited material from the mask, but shadow mask cleaning isgenerally considered incompatible with high volume production ofelectronic devices because most mask cleaning methods are very slow orlabor intensive or would require that the mask be removed from aproduction line and brought to a separate environment for cleaning.

Accordingly, a need exists in this art for equipment and methods torapidly and cost-effectively clean shadow masks in a volumemanufacturing setting. In addition, a need exists for apparatus andmethods for rapidly replacing a used shadow mask for a fresh shadow maskin a manufacturing line.

SUMMARY OF THE INVENTION

The invention is a method of forming an electronic device. The methodincludes (a) sequentially advancing a substrate through a plurality ofvacuum deposition vessels positioned along a fabrication path, whereineach deposition vessel includes (i) a material deposition sourceincluding deposition material, (ii) a first shadow mask positionedwithin the deposition vessel, the first shadow mask having apredetermined pattern of apertures therethrough, (iii) a first cleaningvessel positioned adjacent the deposition vessel, and (iv) a secondcleaning vessel positioned adjacent the deposition vessel, wherein: thefirst cleaning vessel, the deposition vessel and the second cleaningvessel define a cleaning path that is transverse to the fabricationpath; a second shadow mask is positioned in the second cleaning vessel,the second shadow mask having the predetermined pattern of aperturestherethrough; the first cleaning vessel is operative for cleaning thefirst shadow mask when the first shadow mask is received therein; andthe second cleaning vessel is operative for cleaning the second shadowmask when the second shadow mask is received therein; (b) cleaning thesecond shadow mask positioned in the second cleaning vessel concurrentlywith depositing the deposition material through the predeterminedpattern of apertures of the first shadow mask and onto the substrate;(c) moving the first shadow mask along the cleaning path from thedeposition vessel to the first cleaning vessel and moving the secondshadow mask along the cleaning path from the second cleaning vessel tothe deposition vessel; and (d) cleaning the first shadow mask positionedin the first cleaning vessel concurrently with depositing the depositionmaterial through the predetermined pattern of apertures of the secondshadow mask and onto the substrate.

The method can further include (e) moving the second shadow mask alongthe cleaning path from the deposition vessel to the second cleaningvessel and moving the first shadow mask along the cleaning path from thefirst cleaning vessel to the deposition vessel; and (f) repeating step(b)-(e) at least once.

The method can further include advancing the substrate along thefabrication path between deposits of deposition material onto thesubstrate.

The method can further include measuring an end point for cleaning eachshadow mask to indicate when the shadow mask is clean.

The deposition material can be chemically distinct from a chemicalcomponent of each shadow mask.

Each cleaning vessel can include a plurality of cleaning chambers, witheach chamber operative for cleaning a shadow mask.

Each cleaning vessel can include a plasma source or a source of gaseousetchant for cleaning the corresponding shadow mask. The etchant can beselected from either a group consisting of a halogen, ahalogen-containing chemical compound and oxygen or a group consisting ofhydrogen and a hydrogen-containing chemical compound.

The first cleaning vessel and the deposition vessel can beinterconnected by a first vacuum valve. The second cleaning vessel andthe deposition vessel can be interconnected by a second vacuum valve.Moving the first shadow mask can include passing the first shadow maskthrough the first valve. Moving the second shadow mask can includepassing the second shadow mask through the second valve.

The cleaning path can be substantially linear.

The time required for cleaning at least one shadow mask can be eitherless than a time required for depositing the material on the substrateor does not substantially exceed a time required for depositing thematerial on the substrate.

The invention is also a method of forming an electronic devicecomprising (a) providing a substrate adapted for advancement along afabrication path, a first portion of the substrate positioned at a firstprocess location along the path; (b) providing a deposition source fordepositing a material on the substrate at the first process location;(c) providing a first shadow mask and a second shadow mask substantiallyidentical to the first shadow mask; (d) positioning the first shadowmask between the deposition source and the first portion of thesubstrate and positioning the second shadow mask adjacent thefabrication path; (e) depositing the material on the first portion ofthe substrate through the first shadow mask while concurrently cleaningthe second shadow mask; (f) advancing the substrate along thefabrication path whereupon a second portion of the substrate ispositioned at the first process location; (g) positioning the secondshadow mask between the deposition source and the second portion of thesubstrate and positioning the first shadow mask adjacent to thefabrication path; and (h) depositing the material on the second portionof the substrate through the second shadow mask while concurrentlycleaning the first shadow mask.

The material can be deposited and each shadow mask can be cleaned in thepresence of a vacuum.

The method can further include providing a first cleaning vessel forcleaning the first shadow mask and a second cleaning vessel for cleaningthe second shadow mask, wherein each cleaning vessel includes means fordetermining completion of a cleaning process.

Cleaning each shadow mask can include (i) exposing the shadow mask to atleast one of a plasma and a chemical etchant; (ii) reactive ion etching;or (iii) physical sputtering.

The invention is also an apparatus for manufacturing an electronicdevice. The apparatus includes (a) a plurality of interconnecteddeposition vessels defining an elongated fabrication path; (b) means foradvancing a substrate along the fabrication path; (c) at least onematerial deposition source positioned in each deposition vessel fordepositing a material on the substrate when the substrate is positionedin the deposition vessel; and (d) two cleaning vessels connected to eachdeposition vessel, each cleaning vessel operative for receiving a shadowmask from the corresponding deposition vessel for cleaning and forpassing the shadow mask to the corresponding deposition vessel fordepositing the material onto the substrate through a pattern ofapertures in the shadow mask.

Each cleaning vessel can be operative for cleaning the shadow mask byreactive ion etching or by physical sputtering. The substrate can beeither continuous or segmented along the fabrication path.

The apparatus can further include means for monitoring shadow maskcleanliness.

Each cleaning vessel can be connected to its corresponding depositionvessel via a vacuum valve.

The invention is also an apparatus for manufacturing an electronicdevice. The apparatus includes a plurality of vacuum deposition vesselspositioned along a fabrication path and configured for receiving asubstrate advanced along the path and a material deposition sourcepositioned in each deposition vessel. A plurality of shadow masks isprovided and a plurality of shadow mask cleaning vessels are coupled toeach deposition vessel and define therewith a cleaning path thatintersects the fabrication path. For each deposition vessel, onecorresponding cleaning vessel is operative for cleaning one shadow maskwhile the corresponding deposition source is depositing a materialthrough another shadow mask onto a first portion of the substrate andanother cleaning vessel is operative for cleaning the other shadow maskwhile the deposition source is depositing the material through the oneshadow mask onto a second portion of the substrate.

Lastly, the invention is an apparatus for manufacturing an electronicdevice. The apparatus includes a plurality of series connected vacuumdeposition vessels and a material deposition source positioned withineach deposition vessel. Means is/are provided for advancing a substratealong a longitudinal fabrication path through the plurality ofdeposition vessels. A vacuum cleaning vessel is coupled to eachdeposition vessel and a shadow mask is associated with each depositionvessel. Means is/are provided for passing the shadow mask between thedeposition vessel and the corresponding cleaning vessel. The shadow maskis alternately positioned in the cleaning vessel for cleaning the shadowmask, and positioned between the deposition source and the substrate inthe deposition vessel for depositing a material from the materialdeposition source onto the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates schematically in plan view a plurality of processstations in a manufacturing system of the present invention, wherein afirst shadow mask is positioned in a deposition vessels associated witheach station, and a second shadow mask is positioned in a cleaningvessel;

FIG. 1 b illustrates an embodiment of one of the plurality of theprocess stations illustrated in FIG. 1 a;

FIG. 2 illustrates the plurality of stations of FIG. 1 a, wherein usedshadow masks are being replaced with clean shadow masks;

FIG. 3 illustrates the plurality of stations of FIG. 1 a wherein thesecond shadow mask has replaced the first shadow mask in the depositionvessel, and the first shadow mask is positioned in a cleaning vessel;

FIG. 4 illustrates schematically in plan view an embodiment of amulti-mask process station of the present invention;

FIG. 5 illustrates schematically in plan view an embodiment of acarousel process station of the present invention; and

FIG. 6 through FIG. 9 illustrate end views of a process station of thepresent invention and a sequence of process steps for mask cleaningaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the aspects and features of the methods,apparatus, and systems disclosed herein. Examples of these embodimentsand features are illustrated in the drawings. Those of ordinary skill inthe art will understand that the apparatus, systems and methods of usedisclosed herein can be adapted and modified to provide apparatus,systems and methods for other applications and that other additions andmodifications can be made without departing from the scope of thepresent disclosure. For example, the features illustrated or describedas part of one embodiment or one drawing can be used on anotherembodiment or another drawing to yield yet another embodiment. Suchmodifications and variations are intended to be included within thescope of the present disclosure.

The present invention relates to methods, apparatus and systems for themanufacture of electronic devices on substrates, and in particular tothe use of shadow masks in the manufacture of electronic devices, wherecleaning of the masks is integrated into the manufacturing process andapparatus therefor. Some aspects of the apparatus and methods forforming electronic devices using shadow masks are disclosed in U.S. Pat.No. 6,943,066, which is incorporated herein by reference. By electronicdevices, we mean an assembly of electronic elements that may be anycombination of active electronic elements and passive electronicelements formed on a substrate. The active elements may includetransistors, diodes, radiation emitters, sensors or any other type ofactive element. The passive elements may include electrical conductors,resistors, capacitors, inductors or any other type of passive element.By a shadow mask, we mean a sheet of a mask material that is penetratedby a predetermined pattern of apertures, also called vias, through whicha complementary pattern of a deposition material supplied by a vapordeposition source (deposition source) can be deposited onto thesubstrate (also referred to herein as patterning the deposition materialonto the substrate) in a layer that contributes to the formation of theelectronic device. An electronic device may be formed from any number oflayers. Typically, each consecutive patterned layer differs from a layerover which it is patterned with regard to at least one of a depositionmaterial, a mask pattern and a layer thickness.

With reference to FIG. 1 a, an electronic device manufacturing system100 of the present invention includes a plurality of process stations102. FIG. 1 b illustrates a representative one of the plurality ofprocess station 102. Each process station 102 includes a vacuumdeposition vessel 104 positioned along a longitudinal fabrication path106. Each deposition vessel 104 also includes a material depositionsource 108 and a first shadow mask 110 through which a depositionmaterial from deposition source 108 is patterned onto a substrate 112through a pattern of apertures 114 in first shadow mask 110. Depositionsource 108 can be an evaporative source, a sputtering source or anothertype of vacuum deposition source. The deposition material can be anymaterial useful for forming one or more electronic devices on substrate112 and that can be deposited on substrate 112 via deposition source 108and apertures 114 of first shadow mask 110. Examples of depositionmaterials include conductors, semiconductors and insulators. Theinterior of deposition vessel 104 typically is maintained under highvacuum conditions to perform depositions, at pressures typically in therange of 10⁻⁵ torr to 10⁻⁷ torr.

Substrate 112 may be a continuous flexible substrate along fabricationpath 106, or may comprise a longitudinal array of flexible or rigidsubstrate sections along fabrication path 106. Substrate 112 may be anytype of substrate upon which the deposition material can be deposited,including polymer, glass, crystal and metal. Fabrication path 106 may belinear, curved or bent in any manner consistent with advancing substrate112 through the plurality of process stations 102. In one non-limitingembodiment, an unpatterned portion 116 of substrate 112 entersfabrication system 100 at an entrance 118, sequentially receives apatterned layer of a deposition material in the deposition vessel 104 ateach station 102, and leaves fabrication system 100 at an exit 120, withone or more electronic device(s) 122 formed thereon. At each step in thesequence, substrate 112 is advanced along fabrication path 106 so that aportion of substrate 112 moves from one process station 102 to the nextprocess station 102 of the plurality of process stations 102. Eachdeposition of a layer of a deposition material on substrate 112 is anadditive step in forming the one or more electronic device(s) 122.

The plurality of stations 102 may include any number of process stationsrequired to form one or more desired electronic device(s) 122 onsubstrate 112. In one non-limiting embodiment, the plurality of processstations 102 includes six process stations, forming at least one activeelectronic device 122 on substrate 112 by patterning in sequence alongfabrication path 106 a first insulator, a semiconductor, a firstconductor, a second conductor, a second insulator and a third conductor.The electronic device can be a thin-film transistor (TFT) backplane fora flat panel display, wherein the electronic elements of the electronicdevice can be cadmium selenide thin film transistors. The description ofthe electronic device being a TFT backplane, however, is not to beconstrued as limiting the invention since it is envisioned that theplurality of stations 102 of manufacturing system 100 can be utilized toproduce other types of electronic devices.

Each time a shadow mask 110 is used to pattern a deposition materialonto a substrate 112 during a deposition, a layer of the depositionmaterial is also deposited as a film on the surface of the mask (on themask) 110. With each additional deposition through mask 110 ontosubstrate 112, the film on mask 110 increases in thickness, eventuallydegrading the performance of mask 110 as the pattern of apertures 114becomes obscured, distorted, or otherwise changed by the film. Changesin mask 110 due to accumulated deposition material may include fillingof apertures 114 with the deposition material, warping of mask 110,reduced thermal stability of mask 110 due to differential thermalexpansion properties between the film and mask 110, and partial orcomplete delamination of the film from the mask 110. Thus, there is arequirement to periodically replace shadow mask 110 or to clean shadowmask 110 to sustain patterning performance in manufacturing system 100.Frequent replacement of shadow masks 110 is generally economicallyinfeasible in volume manufacturing environments. Therefore, the presentinvention includes methods, apparatus and systems for cleaning shadowmasks 110 for volume manufacturing of electronic devices on substrates.

Shadow masks 110 used for forming layers of deposition materials in themanufacture of electronic devices typically require frequent cleaning.For example, suppose a shadow mask having a 50 micrometer diametercircular aperture therein is used for patterning a substantially 50micrometer diameter, 0.5 micrometer thick pad of a deposition materialon a substrate. If the maximum tolerance of the pad diameter is 10% fromits nominal 50 micrometer diameter, and the deposition material depositsisotropically on the mask surface and inside the aperture during adeposition, each deposition of a pad will reduce the effective innerdiameter of the aperture by one micrometer, whereupon the aperture willdecrease in diameter to its diametric tolerance limit after fivedepositions. To avoid this problem, although a mask may require cleaningonly after a plurality of depositions therethrough, it may be desirableto clean the mask after every deposition. Frequent mask cleaning mayincrease performance consistency between consecutive depositions throughthe mask and may optimize the performance lifetime of a mask byproviding consistent cycling of the mask through deposition and cleaningcycles, as well as by avoiding stresses from accumulated multiple layersof deposited material. An embodiment wherein a shadow mask used forpatterning onto a substrate is exchanged with a clean shadow mask aftereach deposition through the mask will now be described.

Each process station 102 includes a first mask cleaning vessel 124 and asecond mask cleaning vessel 126. Each first cleaning vessel 124 andsecond cleaning vessel 126 is operative for cleaning a mask by removinga film of deposition material from the mask substantially withoutdamaging the mask. In FIGS. 1 a and 1 b, first mask 110 is illustratedpositioned in deposition vessel 104, and a second shadow mask 128 havingthe pattern of apertures 114 is positioned in second cleaning vessel126. Second shadow mask 128 can be substantially identical to firstshadow mask 110. First cleaning vessel 126, deposition vessel 104 andsecond cleaning vessel 128 define a cleaning path 130 along which firstmask 110 and second mask 128 can be translated. Cleaning path 130 can belinear or is folded.

Mask 128 positioned in second cleaning vessel 126 can be cleanedconcurrently with a deposition being performed through first mask 110 indeposition chamber 104. FIGS. 1 a, 2 and 3 illustrate a portion of afabrication process for forming an electronic device in system 100.Following a first deposition of a deposition material in depositionvessel 104 concurrent with the cleaning of second mask 128 in the secondcleaning vessel 126, illustrated in FIGS. 1 a and 1 b, first mask 110 istransported 132 from deposition vessel 104 to first cleaning vessel 124,and second mask 128 is transported 134 from second cleaning vessel 126to deposition vessel 104, as illustrated in FIG. 2.

In addition, as also illustrated in FIG. 2, substrate 112 is advanced ina process direction 136 along fabrication path 106, whereupon a newsection 138 of substrate 112 is introduced to system 100 at entrance 118and a section of substrate bearing one or more completed electronicdevice(s) 122 exits the system 100 at exit 120. When substrate 112 isadvanced in process direction 136, each portion of substrate 112positioned for a deposition in deposition vessel 104 at a first station140 of the plurality of stations 102 is moved and repositioned for anext deposition in the deposition vessel 104 of an adjacent, secondstation 142 of the plurality of stations 102. That is, substrate 112 isadvanced stepwise. In one embodiment, substrate 112 is flexible and isadvanced through the system 100 from a cylindrical supply reel (notshown). In another embodiment, substrate 112 comprises individualsections of substrate material that are advanced individually throughsystem 100. Several means for advancing the substrate along thefabrication path are known in the art, including traction on thesubstrate, conveyor systems and robotic substrate handling systems. Forexample, substrate 112 can be continuous along fabrication path 106 andcan be advanced along fabrication path 106 using traction rollers.

When translation of first mask 110 to first cleaning vessel 124 andsecond mask 128 to deposition vessel 104 is complete and substrate 112has been advanced, as illustrated in FIG. 3, first mask 110 is cleanedin the first cleaning vessel 124 concurrently with a deposition beingperformed in deposition vessel 104 using second mask 128. Following thisdeposition in deposition vessel 104 and the cleaning of first mask 110in first cleaning vessel 124, substrate 112 is again advanced alongfabrication path 106 and the translation direction of first mask 110 andsecond mask 128 along cleaning path 130 is reversed with respect to thetranslation described in association with FIG. 2, whereupon first mask110 is returned to deposition vessel 104 and the second mask 128 isreturned to second cleaning vessel 126. By repeating the above sequence,first mask 110 and second mask 128 are thus cleaned and used forpatterning onto the substrate 112 in an alternating manner. Each processstation 102 can be operated independently or synchronously with regardto which of its respective masks is used for depositing on the substrateor being cleaned at a particular time. For example, whereas FIG. 1 aillustrates all of process stations 102 having their second masks 128being cleaned in second cleaning vessels 126 concurrently withdepositions in deposition vessels 104, in another embodiment, each ofone or more of the plurality of process stations 102 may have its firstmask 110 being cleaned in its corresponding first deposition vessel 124concurrently with a deposition occurring in its corresponding depositionvessel 104, while other process stations 102 have their second masks 128being cleaned in their corresponding second cleaning vessels 126.

A maximum throughput rate (minimum time) for forming electronic devicesusing manufacturing system 100 is determined by the sum of a first,longest time required to perform a deposition in one of process stations102, a second time required to advance a portion of the substrate 112from one process station 102 to a next process station 102 alongfabrication path 106, and a third time required to cycle the portion ofthe substrate 112 through any pressure, temperature and chemicalenvironment changes required for it to be advanced. Desirably, theminimum time is not limited by a time required to clean a mask or by thetime required to cycle a mask between a cleaning vessel and anassociated deposition vessel. That is, a cleaning cycle is desirablyfaster than a deposition cycle. In one embodiment, the time from thebeginning of a deposition onto a first portion of a substrate in adeposition vessel 104 to the beginning of a next deposition on a secondportion of the substrate in deposition vessel 104 (a station cycle time)is less than two minutes. In another embodiment, the cycle time betweendeposition events in the same deposition vessel 104 is less than 30seconds.

In some situations, the time required to clean a mask may exceed thetime required for a deposition. Long cleaning times for masks can beaccommodated in a manufacturing system of the present invention byproviding more than two masks at a process station along a fabricationpath. FIG. 4 illustrates in plan view a multi-mask process station 150of a manufacturing system of the present invention. One or moreprocessed stations 150 can replace a corresponding number of processstations 102 in electronic device manufacturing system 100. Multi-maskstation 150 includes a first cleaning vessel 152 and a second cleaningvessel 154, each having two cleaning chambers 156. A shadow mask 158 isassociated with each cleaning chamber 156, each cleaning chamber 156being adapted for independently cleaning a respective mask 158 and fortransport of the respective mask 158 along a cleaning path 160 betweenthe cleaning chamber 156 and a deposition vessel 162, the depositionvessel 162 being positioned along a fabrication path 164 for advancing asubstrate 166. In addition to the sequence described in association withFIGS. 1-3 for transporting masks alternatingly between cleaning vesselsand a deposition vessel, operation of multi-mask station 150 includes,within each of the first cleaning vessel 152 and the second cleaningvessel 154, alternately transporting a mask 158 from each of the twocleaning chambers 156 thereof to the deposition vessel 162, therebyincreasing the time available to clean each mask 158, since each mask158 is used only every fourth deposition in deposition vessel 162.

In one embodiment, alternately transporting a mask from each of the twocleaning chambers 156 comprises translating 168 the two cleaningchambers 156 as a unit so that the two cleaning chambers 156 arealternately positioned along the cleaning path 160, depending on whichof the two cleaning chambers 156 contains the mask to be next used for adeposition. In FIG. 4 the first cleaning vessel 152 and the secondcleaning vessel 154 are illustrated on opposite ends of cleaning path160. In another embodiment, the two cleaning chambers 156 of each of thefirst cleaning vessel 152 and the second cleaning vessel 154 are fixedin position and each mask 158 is independently transported between eachcleaning chamber 156 and the cleaning path 160, for transport to andfrom the deposition chamber 162.

Another type of multi-mask process station is the mask carousel processstation 200 shown in FIG. 5. Mask carousel station 200 includes a firstcarousel cleaning vessel 202 and a second cleaning vessel 204, with eachcleaning vessel including a plurality of cleaning chambers 206 arrangedabout an axis 208 and having one or more shadow masks 210 associatedtherewith. The plurality of cleaning chambers 206 of each cleaningvessel 202 and 204 is configured to rotate about axis 208 tosequentially position each mask 210 positioned in cleaning chamber 206for transport along a cleaning path 212 that extends between firstcleaning vessel 202 and second cleaning vessel 204 via deposition vessel214. Desirably, more than one mask 210 in at least one of first andsecond cleaning vessels 202 and 204 is cleaned simultaneously.

Cleaning of a shadow mask using methods, apparatus or systems of thepresent invention may be performed using any suitable nondestructivecleaning method compatible with coupling to a means for rapidlytransporting the mask between a cleaning vessel and a vacuum depositionvessel between depositions in the deposition vessel. Suitable cleaningmethods include plasma-based processes such as Reactive Ion Etching(RIE), physical sputtering and ion milling, as well as photochemicaletching, thermal, laser ablative, and chemical etching methods. RIE is achemically selective etching process in which a surface to be cleaned isexposed, under moderate vacuum conditions typically in the range of 20torr to 10⁻³ torr in the cleaning vessel, to a plasma including gaseouschemical species that react rapidly with the material to be removed fromthe mask surface, while reacting much more slowly or being unreactivewith an underlying material. Reaction products are volatile in theplasma environment and pumped away. Physical sputtering is a lesschemically selective plasma process, typically performed at lowerpressures than RIE, with the etching performed by surface collisions ofenergetic but chemically inert chemical species.

Depending on the chemical composition of the mask and of the material tobe removed, RIE gases typically are gaseous or volatilizable chemicalcompounds, or elemental oxidizing gases including fluorine, chlorine,bromine, iodine and oxygen, or reducing gases including hydrogen andhydrogen-containing compounds. Masks may be made from any material thatcan be fabricated as a thin sheet having a pattern of apertures suitablefor patterning a deposition material onto a substrate, and maskconstruction materials may be selected for inertness under RIE, relativeto an etching gas. Thus, it may be desirable to manufacture masks fromdifferent materials to pattern different layers in the formation of anelectronic device, depending on a desired cleaning chemistry. Typically,masks are metallic, manufactured from pure metals or alloys. Common maskmaterials include nickel, copper, and refractory metals.

Referring again to FIGS. 1-3, the pressure and the chemical environmentwithin each deposition vessel 104 is generally different from thepressure and the chemical environment within an associated first and/orsecond cleaning vessels 124, 126. In addition, each process station 102may require a deposition material that is different from a depositionmaterial required for deposition at an adjacent process station 102along the fabrication path 106. To maintain these differences inenvironment, the fabrication system 100 includes suitable means toisolate the internal working environments of each deposition vessel 104and its corresponding first and second cleaning vessels 124, 126.

Deposition vessel 104 of each process station 102 along fabrication path106 is isolated from deposition vessel 104 in an adjacent processstation 102 by a station separation means 250 through which substrate112 can be translated. In one non-limiting embodiment, stationseparation means 250 is a vacuum valve that is closed between separatesections of substrate 112 along the fabrication path 106 during adeposition. Also or alternatively, where substrate 112 is continuousalong fabrication path 106, the vacuum valve seals one or more surfacesof substrates 112. Desirably, the vacuum valve is adapted for rapidopening and closure, and adjacent deposition vessels are atsubstantially the same pressure as one another before the vacuum valveis opened. In one embodiment, the vacuum valve is a gate valve.

In another embodiment, depositions in adjacent deposition vessels 104are performed at a similar pressure and separation means 250 is asubstantially slot-shaped opening through which substrate 112 istranslated along fabrication path 106. In a further embodiment,separation means 250 is ported to a vacuum source to support theisolation of deposition vessels 104 in adjacent process stations 102. Inanother embodiment, each separation means 250 is ported to a separatevacuum source so that a plurality of separation means 250 can bedifferentially pumped along the fabrication path 106.

Each cleaning vessel 124, 126 is isolated from its associated depositionvessel 104 by a vacuum valve 252 through which a mask can be translated.Each vacuum valve 252 can be ported to a vacuum source to enhanceisolation of deposition vessel 104 from its corresponding cleaningvessels 124, 126. In another embodiment, each vacuum valve 252 is portedto a separate vacuum source so that a plurality of vacuum valves 252 canbe differentially pumped along cleaning path 130. In one embodiment,vacuum valve 252 is a load lock.

FIG. 6 illustrates another embodiment of a process station 300 of thepresent invention. Process station 300 includes a deposition vessel 302,a first cleaning vessel 304, a second cleaning vessel 306, a first valve308 for isolating the first cleaning vessel 304 from the depositionvessel 302 and a second valve 310 for isolating the second cleaningvessel 306 from the deposition vessel 302. Deposition vessel 302 ispositioned along a fabrication path 311 (out of the plane of FIG. 6).

Deposition vessel 300 includes a first shadow mask 312 and depositionsource 314 adapted for patterning a deposition material 316 through mask312 onto a substrate 317. Deposition vessel 302 is ported to a vacuumsource 318 for establishing and maintaining vacuum for performingdepositions. Each cleaning vessel 304 and 306 includes a cleaning means320. In one embodiment, cleaning means 320 is RIE. In anotherembodiment, cleaning means 320 is physical sputtering. Each cleaningvessel 304 and 306 is ported to a corresponding vacuum source 322. Asecond shadow mask 324 is shown positioned in second cleaning vessel 306for removing deposited material 326 from second mask 324. As second mask324 is cleaned, removed material 326 is pumped from second cleaningvessel 306 by its corresponding vacuum source 322.

Each of first valve 308 and second valve 310 is ported to acorresponding vacuum source 328 for enhancing the isolation ofrespective first and second cleaning vessels 304 and 306 from depositionvessel 302. Each cleaning vessel 304, 306 is adapted for at least one ofrapid flushing with a purging gas, and rapid pumpdown from a pressureused for mask cleaning, to a lower pressure suitable for performance ofa deposition in deposition vessel 302.

FIGS. 6-9 illustrate an exemplary cycle of exchanging masks amongdeposition chamber 302, first cleaning vessel 304 and second cleaningvessel 306 during time intervals between depositions in depositionvessel 302. Referring to FIG. 6, station 300 includes first mask 312positioned in deposition vessel 302 and second mask 324 positioned insecond cleaning vessel 306. In FIG. 6, a first deposition is in progressin deposition vessel 302 concurrently with cleaning second mask 324 insecond cleaning vessel 306. First and second valves 308 and 310 areclosed. Turning now to FIG. 7, following completion of the firstdeposition, first and second valves 308 and 310 are opened. First mask312 is then transported 332 through first valve 308 from depositionvessel 302 to first cleaning vessel 304 and second mask 324 istransported 332 through second valve 310 from second cleaning vessel 306to deposition vessel 302. Transport of first and second masks 312 and314 may be by any suitable means compatible with transport of a thin,flat object under vacuum through a vacuum valve, including conveyorbelts, rollers, robotic arms or other mechanical means.

For maximum throughput in a manufacturing system of the presentinvention for volume manufacturing of electronic devices, it isgenerally preferred that mask cleaning does not limit the productionspeed. To this end, the cleaning of second mask 324 is completed andboth first and second cleaning vessels 304 and 306 are pumped down tosubstantially the pressure in deposition vessel 302 before first andsecond valves 308 and 310 are opened. In another embodiment, an endpoint detection means is included in each cleaning vessel 304 and 306.End point detection supports maximum throughput of manufacturing system300 by signaling manufacturing system 300 to stop cleaning a mask asearly as possible. End point detection also provides quality control forthe cleaning process, preventing either incomplete cleaning of a mask,or erosion of a mask associated with overcleaning, for example, byunnecessarily long exposure to a plasma.

Suitable technologies for end-point detection include any technologythat can sense the presence of a predetermined deposition material on amask surface. In one embodiment, end point detection uses an opticalsensor to monitor changes in the emission spectrum of plasma above thesurface being cleaned, as a deposition material is removed from thesurface into the plasma. In another embodiment, a cleaning end point isdetermined using at least one of spectroscopic absorption, fluorescenceand scattering measurements of electromagnetic radiation introduced intoa cleaning vessel from an external radiation source. In yet anotherembodiment, measurement of an electrical characteristic of the plasma isused to detect an end point of a cleaning process. In still anotherembodiment, an end point is determined by measuring a physical referencemark on, or aperture through a mask being cleaned. In yet anotherembodiment, a mask includes a chemical component added as an indicatorto a material from which the mask is constructed to assist in end pointdetection.

In one embodiment, substrate 317 is advanced along fabrication path 311concurrently with transport of first and second masks 312 and 324 amongfirst cleaning vessel 304, deposition vessel 302 and second cleaningvessel 306. In another embodiment, advancing substrate 317 andtransporting first and second masks 312 and 324 are performedsequentially. Desirably, the pressure in deposition vessel 302 ismaintained substantially constant during transport of first and secondmasks 312 and 324. Turning now to FIG. 8, first mask 312 is positionedin first cleaning vessel 304, second mask 324 is positioned indeposition vessel 302, and first and second valves 308 and 310 have beenclosed 330. Cleaning of first mask 312 in first cleaning vessel 304 isin progress concurrently with a second deposition occurring indeposition vessel 302. Turning finally to FIG. 9, after completion ofthe second deposition using second mask 324 and cleaning of first mask312, first and second masks 312 and 324 are transported in a direction334 opposite the transport 332 illustrated in FIG. 7, returning firstmask 312 to deposition vessel 302 and second mask 324 to second cleaningvessel 306, as illustrated in FIG. 6.

Embodiments of the present invention have many advantages, including,but not limited to, advantages associated with enhancedmanufacturability of electronic devices and reduced cost of fabricationfacilities for electronic devices, particularly for large areaelectronic devices. A fabrication system of the present invention isscalable in a straightforward manner to producing electronic devices onvery large substrates, limited primarily by the manufacturability oflarge area shadow masks. Further, by cleaning the shadow masksfrequently and in proximity to a deposition vessel, manufacturing speedis optimized, the performance of the shadow masks is maintained overmany deposition cycles, and the risk of damaging a mask associated withtransporting the mask elsewhere for cleaning is eliminated. In addition,and particularly for multi-mask and carousel embodiments of the presentinvention, the inherent redundancy of using a plurality of masks at eachprocess station enables replacement of a failed or worn mask withoutstopping a production line, by replacing the mask during the time itwould have been cleaned.

Another advantage of electronic device manufacturing systems and methodsof the present invention is its unity of manufacturing technology.Unlike photolithographic manufacturing facilities that employ manydisparate manufacturing technologies and many types of manufacturingequipment to produce a single type of electronic device, a manufacturingsystem of the present invention employs only material deposition andrelated mask cleaning technologies to produce an electronic device. Thisunity of technology will enable manufacturing facilities to beconstructed for substantially lower cost than present photolithographicmanufacturing facilities. Yet another advantage of the present inventionis that it provides an electronic device manufacturing system that doesnot have to be completely enclosed in a clean room environment, sincemost or all manufacturing steps for the electronic devices are performedin a series of interconnected vacuum vessels.

The invention has been described with reference to the preferredembodiment. Obvious modifications and alterations will occur to othersupon reading and understanding the preceding detailed description. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

1. A method of forming an electronic device comprising: (a) sequentiallyadvancing a substrate through a plurality of vacuum deposition vesselspositioned along a fabrication path, wherein each deposition vesselincludes (i) a material deposition source including deposition material,(ii) a first shadow mask positioned within the deposition vessel, thefirst shadow mask having a predetermined pattern of aperturestherethrough, (iii) a first cleaning vessel positioned adjacent thedeposition vessel, and (iv) a second cleaning vessel positioned adjacentthe deposition vessel, wherein: the first cleaning vessel, thedeposition vessel and the second cleaning vessel define a cleaning paththat is transverse to the fabrication path; a second shadow mask ispositioned in the second cleaning vessel, the second shadow mask havingthe predetermined pattern of apertures therethrough; the first cleaningvessel is operative for cleaning the first shadow mask when the firstshadow mask is received therein; and the second cleaning vessel isoperative for cleaning the second shadow mask when the second shadowmask is received therein; (b) cleaning the second shadow mask positionedin the second cleaning vessel concurrently with depositing thedeposition material through the predetermined pattern of apertures ofthe first shadow mask and onto the substrate; (c) moving the firstshadow mask along the cleaning path from the deposition vessel to thefirst cleaning vessel and moving the second shadow mask along thecleaning path from the second cleaning vessel to the deposition vessel;and (d) cleaning the first shadow mask positioned in the first cleaningvessel concurrently with depositing the deposition material through thepredetermined pattern of apertures of the second shadow mask and ontothe substrate.
 2. The method of claim 1, further including: (e) movingthe second shadow mask along the cleaning path from the depositionvessel to the second cleaning vessel and moving the first shadow maskalong the cleaning path from the first cleaning vessel to the depositionvessel; and (f) repeating step (b)-(e) at least once.
 3. The method ofclaim 2, further including advancing the substrate along the fabricationpath between deposits of deposition material onto the substrate.
 4. Themethod of claim 1, further comprising measuring an end point forcleaning each shadow mask to indicate when the shadow mask is clean. 5.The method of claim 1, wherein the deposition material is chemicallydistinct from a chemical component of each shadow mask.
 6. The method ofclaim 1, wherein each cleaning vessel includes a plurality of cleaningchambers, each chamber operative for cleaning a shadow mask.
 7. Themethod of claim 1, wherein each cleaning vessel includes a plasma sourceor a source of gaseous etchant for cleaning the corresponding shadowmask.
 8. The method of claim 7, wherein the etchant is selected fromeither: a group consisting of a halogen, a halogen-containing chemicalcompound and oxygen; or a group consisting of hydrogen and ahydrogen-containing chemical compound.
 9. The method of claim 1,wherein: the first cleaning vessel and the deposition vessel areinterconnected by a first vacuum valve; the second cleaning vessel andthe deposition vessel are interconnected by a second vacuum valve;moving the first shadow mask includes passing the first shadow maskthrough the first valve; and moving the second shadow mask includespassing the second shadow mask through the second valve.
 10. The methodof claim 1, wherein the cleaning path is substantially linear.
 11. Themethod of claim 1, wherein a time required for cleaning at least oneshadow mask is either: less than a time required for depositing thematerial on the substrate; or does not substantially exceed a timerequired for depositing the material on the substrate.
 12. A method offorming an electronic device comprising: (a) providing a substrateadapted for advancement along a fabrication path, a first portion of thesubstrate positioned at a first process location along the path; (b)providing a deposition source for depositing a material on the substrateat the first process location; (c) providing a first shadow mask and asecond shadow mask substantially identical to the first shadow mask; (d)positioning the first shadow mask between the deposition source and thefirst portion of the substrate and positioning the second shadow maskadjacent the fabrication path; (e) depositing the material on the firstportion of the substrate through the first shadow mask whileconcurrently cleaning the second shadow mask; (f) advancing thesubstrate along the fabrication path whereupon a second portion of thesubstrate is positioned at the first process location; (g) positioningthe second shadow mask between the deposition source and the secondportion of the substrate and positioning the first shadow mask adjacentto the fabrication path; and (h) depositing the material on the secondportion of the substrate through the second shadow mask whileconcurrently cleaning the first shadow mask.
 13. The method of claim 12,wherein the material is deposited and each shadow mask is cleaned in thepresence of a vacuum.
 14. The method of claim 12, further comprisingproviding a first cleaning vessel for cleaning the first shadow mask anda second cleaning vessel for cleaning the second shadow mask, whereineach cleaning vessel includes means for determining completion of acleaning process.
 15. The method of claim 12, wherein cleaning eachshadow mask comprises (i) exposing the shadow mask to at least one of aplasma and a chemical etchant, (ii) reactive ion etching or (iii)physical sputtering.
 16. The method of claim 12, wherein a time requiredfor cleaning either shadow mask is either: less than a time required fordepositing the material on the substrate; or does not substantiallyexceed a time required for depositing the material on the substrate.